In the field of medical treatment such as ophthalmology, a refractive power measurement device which measures the eye refractive power has been widely used. An example of the refractive power measurement device is a refractive power measurement device using retinoscopy such as the types disclosed in patent documents 1 and 2. In the field of medical treatment including ophthalmology, measurement of the eye accommodation function state has also been demanded as a more detailed refraction state. For example, a device which objectively measures the eye accommodation function state has been proposed, such as an eye accommodation function state measurement device disclosed in patent document 3.
In eye accommodation function state measurement, the eye refractive power is continuously measured at high speed by utilizing a known refractive power measurement method (e.g. method disclosed in the patent document 2). Therefore, since an eye accommodation function state measurement device is generally similar to a known eve refractive power measurement device, a compound device enabling normal eye refractive power measurement (hereinafter may be called normal measurement) and eye accommodation function state measurement increases efficiency and convenience.    (Patent document 1) JP-A-55-160538    (Patent document 2) JP-A-6-165757    (Patent document 3) JP-A-2003-70740
According to the patent document 3, an eye accommodation function state measurement device must continuously measure the refractive power at a frequency of 1 Hz to 2.3 Hz. An eye refractive power measurement section can obtain measurement values at measurement intervals of 0.1 second when the frequency is set at 1 Hz, and can obtain measurement values at measurement intervals of 0.05 seconds when the frequency is set at 2 Hz. And in the meantime the high-frequency components cannot to be obtained unless the measurements are continuously performed. However, a known eye refractive power measurement device requires a measurement time of at least about 0.2 seconds per measurement. Therefore, since it is difficult to directly apply a known eye refractive power measurement device to an eye accommodation function state measurement device, an eye refractive power measurement device must be improved or modified so that continuous measurement can be performed at higher speed.
For example, when using the refractive power measurement method disclosed in the patent document 1, an optical system including a prism is caused to make a round by a motor in parallel to the meridian direction in order to measure the eye refractive power in all meridian directions. In order to measure the refractive power within 0.1 second or less per measurement, the optical system must be rotated at a higher speed than in a known device. Therefore, the size of the motor must be increased in order to increase the rotational speed of the motor, the rigidity of the device must be increased in order to allow continuous rotation, or a high-speed processing circuit is required in order to perform high-speed measurement processing. This results in an increase in size and cost in comparison with a known device.
A compound device may suffer from a display difficulty if the normal refractive power measurement is performed at high speed in the same manner as the eye accommodation function state measurement device. Therefore, operability (convenience) may be decreased due to an increase in speed.